Molecular sieve materials, both natural and synthetic, have been demonstrated in the past to be useful as adsorbents and to have catalytic properties for various types of hydrocarbon conversion reactions. Certain molecular sieves, such as zeolites, aluminosphosphates, and mesoporous materials, are ordered, porous crystalline materials having a definite crystalline structure as determined by X-ray diffraction (XRD). Within the crystalline molecular sieve material there are a large number of cavities which may be interconnected by a number of channels or pores. These cavities and pores are uniform in size within a specific molecular sieve material. Because the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as “molecular sieves” and are utilized in a variety of industrial processes.
High-silica zeolite SSZ-31 is a highly faulted molecular sieve material having one-dimensional 12-membered ring pores with pore dimensions of approximately 8.6 Å×5.7 Å. The framework structure of SSZ-31 has been assigned the three-letter code *STO by the Structure Commission of the International Zeolite Association.
The composition and characterizing powder X-ray diffraction pattern of SSZ-31 are disclosed in U.S. Pat. No. 5,106,801, which also describes the synthesis of the borosilicate form of the zeolite in the presence of a structure directing agent selected from N,N,N-trimethylammonium-8-tricyclo[5.2.1.0]decane, 4-trimethylammonium-2,2,6,6-tetramethylpiperidine, N,N-dimethyl-3-azonium bicyclo[3.2.2]nonane, N,N,N-trimethylammonium-2-bicyclo[3.2.1]octane, N,N-dimethyl-6-azonium-1,3,3-trimethylbicyclo[3.2.1]octane, and N,N,3,5,5-pentamethyl azonium cycloheptane. An all-silica form of SSZ-31 was synthesized using N,N,N-trimethylammonium-8-tricyclo[5.2.1.0]decane as a structure directing agent.
Due to the very large pore diameter of SSZ-31, forms of SSZ-31 with aluminum incorporated into the zeolite framework structure are of interest for shape-selective catalysis, such as the alkylation of relatively bulky aromatic compounds.
Aluminosilicate SSZ-31 (Al-SSZ-31) may be prepared indirectly from borosilicate SSZ-31 (B-SSZ-31) by heteroatom lattice substitution techniques such as described in U.S. Pat. No. 5,106,801.
U.S. Pat. No. 6,471,940 discloses the direct synthesis of Al-SSZ-31 by a dry-gel conversion method using a structure directing agent selected from hexamethylene bis(triethylammonium hydroxide), heptamethylene bis(triethylammonium hydroxide), octamethylene bis(triethylammonium hydroxide), nonamethylene bis(triethylammonium hydroxide), and decamethylene bis(triethylammonium hydroxide).
R. K. Ahedi et al. (J. Mater. Chem. 2001, 11, 2922-2924) report the direct synthesis of Al-SSZ-31 from Al-BEA precursors by a hydrothermal route using hexamethylene bis(triethylammonium hydroxide) as a structure directing agent.
According to the present disclosure, it has now been found that 2-ethyl-N,N,N-trimethylbutan-1-aminium cations are effective as a structure directing agent in the direct synthesis of all-silica and aluminosilicate forms of zeolite SSZ-31.